Hydraulic steering systems typically include a user interface pump (e.g., a yolk or a helm pump) connected to a steering cylinder or other type of hydraulic actuator that is used to change the position of a steering control surface, such as a rudder and/or an articulated propulsion system/outboard motor on a ship or an airplane. Conventional autopilot installations for hydraulic systems add a motorized reversing autopilot pump and a reference transducer or sensor coupled to the steering control surface to provide accurate steering angles/positions as feedback to the autopilot controller. The disconnect between the speed of a hydraulic pump motor and the rate of movement of a coupled hydraulic actuator is often so significant and variable that a reference transducer/sensor is necessary for reliable autopilot control.
Unfortunately, reference transducers/sensors are typically expensive, fragile, and difficult to install and maintain, particularly with respect to open vehicles or other mobile structures, such as power boats, that do not or cannot provide a dry, enclosed, or otherwise protected space around an outboard motor, tiller assembly, and/or steering cylinder. Mechanically steered autopilot installations can operate successfully without a reference transducer/sensor, because steering angles/positions can be estimated reliably and with sufficient accuracy by integrating a mechanically linked motor speed and using known gearing ratios between the motor and the steering angle, but mechanical steering systems can also be fragile and difficult to maintain and/or repair, and they are often limited for use with relatively small mobile structures.
Thus, there is a need for an improved methodology to provide inexpensive, accurate, and reliable positioning for a hydraulic actuator, particularly in the context of a hydraulic actuator used to steer a mobile structure.